1. Field of the Invention
An embodiment of the present invention applies to the field of digital photography and, in particular, to correcting digital images.
2. Description of the Prior Art
Digital photography is the process of capturing, processing, and rendering images digitally. Digital representation of images, which means that images are represented by a finite number of pixels (Picture Elements) where each pixel can assume a finite number of values, is well known in the art. Capturing digital images by using, for example, digital cameras or scanners is also well known. One advantage of digital photography over traditional analog photography is that a general-purpose computer, or specialized circuit, can process the images captured digitally. Such processing may include color correction, redeye removal, intentional distortion to create “special” effects, and changing or correcting various other characteristics of the image.
One characteristic of a digital image that may need correcting is color. Color correcting involves a user manipulating the image, with or without automatic calculations by a computer, to make the colors on the image closer to what the user is looking for. There are several color-correcting schemes known in the art.
One such scheme requires that the user identify an object with a known color-range in the image to be corrected. For example, the user could use a mouse to click on a portion of a digital image representing a person. The computer would then compare the skin tone colors of that person to a color-range known for human skin, that is, the usual range of colors skin takes on. For example, if skin appears blue in an image, the computer—or the person performing the correction by hand—will know that corrections must occur. Other schemes relying on general information about what certain objects, such as humans, sky, plants, and so on also exist. For example, the product known as iCorrect produced by Pictograpics uses this general type of technique.
One limitation of these techniques is that they rely on a range of colors to perform the correction, and are thus limited in accuracy by this range. For example, it is true that skin cannot be blue, but it can be a broad range between pale white and dark black. Even excluding people of African descent, it is clear that relying on the range of expected skin colors for people, or other general objects, is limited in accuracy.
However, the range of colors for a specific person, or specific object, does not vary quite as much. For example, the skin tone of an individual varies much less than the skin range within even a single ethnicity of people. Furthermore, most of the variation in color for individual people is seasonal. The prior art schemes have not exploited this, and no correction scheme relies on specific and unique subjects in images, such as a specific person, or a specific tree, for digital image correction.